The Gallinas Canyon Gneiss: a window into the nature and timing of Paleoproterozoic events in northern New Mexico
D. Lemen, J. Lindline, and H. Bosbyshell
The paucity of evidence of pre-1450 Ma tectonism in northern New Mexico limits the understanding of Paleoproterozoic magmatism, metamorphism, and deformation and correlating events regionally. Here, we report new field, petrographic, geochemical, and geochronological data from metamorphic rocks from the Gallinas Canyon area in the southern Sangre de Cristo Mountains of New Mexico that preserve evidence for 1.7 Ga tectonothermal metamorphism. Gallinas Canyon area metamorphic rocks include medium-grained quartzofeldspathic gneiss, amphibolitic gneiss, biotite schist, and granitic pegmatite. The units are in many places strongly layered and penetratively foliated with a dominant fabric dipping moderately to the southwest. Mafic units (amphibolite and biotite schist) show igneous differentiation trends and major and trace element characteristics of island arc tholeiites and ocean island arc basalts. All of these units were deformed and metamorphosed at upper-amphibolite facies (725°C, 550 MPa). Zircons from an amphibolite sample showed soccer ball morphologies and high (>10) elemental U/Th ratios indicative of metamorphic zircon. U-Pb isotopic analyses of this zircon population yielded an age of 1717 ±14 Ma, which we ascribe to amphibolite facies metamorphism during syntectonic emplacement of the ca. 1.7 Ga Hermit Peak granite. These data document Yavapai province arc-related magmatism, metamorphism, and deformation in northern New Mexico.
- Lemen, D.; Lindline, J.; Bosbyshell, H., 2015, The Gallinas Canyon Gneiss: a window into the nature and timing of Paleoproterozoic events in northern New Mexico, in: Geology of the Las Vegas Region, , New Mexico Geological Society, Guidebook, 66th Field Conference, pp. 185-192.